Field of the Invention
The present invention relates to a solventless type hardenable or curable resin composition. More particularly, the present invention is concerned with an oil modified alkyd resin composition which can be dried at room temperature and hardened by baking and is capable of providing a film having excellent surface smoothness, hardness, and adhesiveness to metals and woods.
Oil-modified alkyd resins are, in general, prepared from polybasic acids, polyhydric alcohols, and unsaturated fatty acids. Because the double bond in the unsaturated fatty acids of the resin constituents tends to take part in a cross-linking reaction in the presence of oxygen in air thereby to harden the resins, they have been used in various paints such as room temperature drying paints and baking paints.
Considering that the fatty acid in the oil-modified alkyd resin reacts with glycerin to form a triglyceride, the weight percentage of the formed triglyceride present in the resin is called an oil length. The oil length is an important indication of the physical properties of a paint. That is, the solubility, hardness, gloss, color preserving ability, weather resistance, hardening time, and storage life of a paint are estimated on the basis of the oil length. For example, an increase in oil length has the effect of enhancing the flexibility and solubility in organic solvents of a paint film, while it tends to decrease the hardness of the film. On the other hand, a reduction in oil length results in an enhancement of the gloss and color preserving ability of the film, while it tends to decrease the extensibility of a paint. It is to be understood, of course, that the oil length is not the only factor influencing the physical properties of the paint, and that these properties depend also upon the nature of the other constituents of the oil-modified alkyd resin.
Conventional oil-modified alkyd resins have an oil length of the order of 30 to 80% and are generally dissolved in a solvent such as turpentine oil and toluene to be used as a room temperature drying paint or baking paint. However, an oil-modified alkyd resin paint of this character diluted with a solvent requires a long drying time, and, moreover, the solvent vaporized during drying pollutes the working environment.
Alkyd resin paints using no solvent, i.e., those of the solventless type (also called non-pollution type) paints wherein all the paint constituents contained in the paints react have been proposed. These paints have not only poor adhesion to metals but also poor mechanical properties such as impact resistance and flexure resistance. Furthermore, their spreadability is inferior. Accordingly, these paints have not yet been put to practical use.